Using helium, hydrogen, nitrogen, etc. instead of CFCs as working gas, the Stirling engine has been attracting much attention as a heat engine that does not destroy the ozone layer. Examples of the Stirling engine are seen in Patent Publications 1 to 4 listed below.    Patent Publication 1: Japanese Patent Application Laid-open No. 2000-337725 (pages 2 to 4, FIGS. 1 to 4)    Patent Publication 2: Japanese Patent Application Laid-open No. 2001-231239 (pages 2 to 4, FIGS. 1 to 4)    Patent Publication 3: Japanese Patent Application Laid-open No. 2002-213831 (pages 3 to 4, FIG. 1)    Patent Publication 4: Japanese Patent Application Laid-open No. 2002-349347 (pages 5 to 6, FIGS. 1 to 4)